Welcome to the Yocto Project Software Development Kit (SDK) Developer's Guide. This manual provides information that explains how to use both the standard Yocto Project SDK and an extensible SDK to develop applications and images using the Yocto Project. Additionally, the manual also provides information on how to use the popular Eclipse™ IDE as part of your application development workflow within the SDK environment.
Prior to the 2.0 Release of the Yocto Project, application development was primarily accomplished through the use of the Application Development Toolkit (ADT) and the availability of stand-alone cross-development toolchains and other tools. With the 2.1 Release of the Yocto Project, application development has transitioned to within a more traditional SDK and extensible SDK.
A standard SDK consists of the following:
Cross-Development Toolchain: This toolchain contains a compiler, debugger, and various miscellaneous tools.
Libraries, Headers, and Symbols: The libraries, headers, and symbols are specific to the image (i.e. they match the image).
Environment Setup Script:
This *.sh
file, once run, sets up the
cross-development environment by defining variables and
preparing for SDK use.
You can use the standard SDK to independently develop and test code that is destined to run on some target machine.
An extensible SDK consists of everything that the standard SDK has plus tools that allow you to easily add new applications and libraries to an image, modify the source of an existing component, test changes on the target hardware, and easily integrate an application into the OpenEmbedded build system.
SDKs are completely self-contained.
The binaries are linked against their own copy of
libc
, which results in no dependencies
on the target system.
To achieve this, the pointer to the dynamic loader is
configured at install time since that path cannot be dynamically
altered.
This is the reason for a wrapper around the
populate_sdk
and
populate_sdk_ext
archives.
Another feature for the SDKs is that only one set of cross-compiler
toolchain binaries are produced per architecture.
This feature takes advantage of the fact that the target hardware can
be passed to gcc
as a set of compiler options.
Those options are set up by the environment script and contained in
variables such as
CC
and
LD
.
This reduces the space needed for the tools.
Understand, however, that a sysroot is still needed for every target
since those binaries are target-specific.
The SDK development environment consists of the following:
The self-contained SDK, which is an architecture-specific cross-toolchain and matching sysroots (target and native) all built by the OpenEmbedded build system (e.g. the SDK). The toolchain and sysroots are based on a Metadata configuration and extensions, which allows you to cross-develop on the host machine for the target hardware.
The Quick EMUlator (QEMU), which lets you simulate target hardware. QEMU is not literally part of the SDK. You must build and include this emulator separately. However, QEMU plays an important role in the development process that revolves around use of the SDK.
The Eclipse IDE Yocto Plug-in. This plug-in is available for you if you are an Eclipse user. In the same manner as QEMU, the plug-in is not literally part of the SDK but is rather available for use as part of the development process.
Various user-space tools that greatly enhance your application development experience. These tools are also separate from the actual SDK but can be independently obtained and used in the development process.